1. Field of the Invention
The present invention relates to a heating apparatus including a ceramic heater.
2. Description of the Related Art
FIG. 1A is a cross-sectional view illustrating a heating apparatus including a ceramic heater according to the related art, and FIG. 1B is a perspective view illustrating a ceramic heater according to the related art.
Referring to FIGS. 1A and 1B, a heating apparatus 1 includes a housing 10, a ceramic heater 20 installed inside the housing 10, and a fixing member 30 fixing the ceramic heater 20 to the housing 10.
The housing 10 and the ceramic heater 20 have cylindrical shapes and are disposed coaxially in general. The fixing member 30 has an inlet hole communicating with the inner space of the ceramic heater 20, and the housing 10 has an outlet hole. Accordingly, water introduced through the inlet hole passes through the inner space of the ceramic heater 20, flows along the outside space of the ceramic heater 20, and is discharged through the water outlet. Water, when flowing through the inner space of the ceramic heater 20, is heated by contacting the inner wall of the ceramic heater 20. When flowing through the outside space of the ceramic heater 20, the water is heated by contacting the outer wall of the ceramic heater 20. The water heated in the above manner is discharged through the outlet hole.
However, as shown in FIG. 1B, a heating wire 22, installed inside the ceramic heater 20 according to the related art, is placed adjacent to the outer wall of the ceramic heater 20. For this reason, water is heated mostly by the outer wall, while the inner wall rarely contributes to heating water. Thus, water introduced into the heating apparatus 1 is heated mostly when flowing through the outside space of the ceramic heater 20. This substantially reduces the time for which water is heated. In order to acquire warm water of high temperature, high power needs to be applied to the heating wire 22 of the ceramic heater 20, which is undesirable in terms of energy efficiency.
In this regard, Korean Patent Registration No. 0880773 suggests a fluid heating apparatus ensuring enhanced heating efficiency. As for the concrete construction thereof, the fluid heating apparatus includes flat ceramic heaters 102, spacer plates 105, channel forming plates 106, an upper cover 111 and a lower cover 113. The flat ceramic heaters 102 each have a terminal lead line 101 for power application. The spacer plates 105 are respectively disposed on and under the ceramic heater 102 in such a manner as to provide horizontal fluid paths. The horizontal fluid paths allow a fluid, which is to be heated, to flow toward the ceramic heater 102 while allowing a fluid heated by the ceramic heater 102 to be discharged. The channel forming plates 106 provide fluid channels such that a fluid, having passed through the horizontal fluid path, moves vertically toward the next fluid path. The upper cover 111 is coupled to the outer surface of the uppermost spacer plate 105 and has an inlet hole 110 through which a fluid to be heated is supplied. The lower cover 113 is coupled to the outer surface of the lowermost spacer plate 105 and has an outlet hole 112 through which a heated fluid is discharged.
According to the configuration suggested in the above document, the flat ceramic heater 102 is installed, and the spacer plates 105 and the channel forming plates 106 are disposed so as to form fluid paths on and under the ceramic heater 102. Accordingly, water introduced through the inlet hole 110 is instantaneously heated while contacting the upper and lower surfaces of the ceramic heater 120, and is then discharged through the outlet hole 112. By this construction, heat transfer occurs while water is in contact with a wide area of the flat ceramic heater 102, thereby enhancing heating efficiency.
However, the following limitations are present in the construction disclosed in the above-mentioned document where the flat ceramic heaters 102 are disposed horizontally and water is directed from the inlet hole 110 provided in the upper part toward the outlet hole 112 provided in the lower part.
FIG. 2 illustrates a flow path of the fluid heating apparatus configured as above. Referring to FIG. 2, it can be seen that water, introduced from the inlet hole 110 in the upper portion, passes through the flat ceramic heater 102 and is discharged through the outlet hole 112 provided in the lower portion. Water, when flowing along the upper surface of the ceramic heater 102, is heated by constantly contacting the ceramic heater 102. However, when flowing along the lower surface of the ceramic heater 102, water may not be in contact with the ceramic heater (See a portion indicated by a circle in the drawing). Of course, if a large amount of water is injected with high pressure, water may flow, fully occupying the entire flow path. However, if a small amount of water is provided or water pressure is low, water may not fully occupy the entire flow path. In that case, water, flowing through the flow path formed under the ceramic heater 102, may fail to contact the ceramic heater 102 as indicated by the circle in FIG. 2.
When water flows without making contact with the ceramic heater 102, the following limitations may arise.
First, water failing to contact the ceramic heater 102 wastes heat and degrades heating efficiency.
Secondly, in the flow path where water fails to contact the ceramic heater 102, air may come into contact with the ceramic heater 102 instead of water and be rapidly heated, thereby causing a drastic temperature change and accordingly thermal impact. Since the ceramic heater 102 is susceptible to thermal impact, a device may be easily damaged.
Thirdly, when a large amount of water is provided and water pressure is high, water flows while occupying the entire flow path to thereby increase heating efficiency. However, when a small amount of water is introduced and water pressure is low, water may not come into contact with a portion of the ceramic heater 102 to thereby degrade heating efficiency. For this reason, constant heating efficiency and accurate control may not be ensured.
Fourthly, even in the case in which a large amount of water is provided, water pressure is high and therefore water fully occupies the entire flow path, water heated by a heating surface, i.e., an increase in water temperature, may decrease the solubility of gases, dissolved in the water, and the gases are thus eluted. Accordingly, bubbles are generated, resulting in thermal impact. According to this document, the cross-section of a heating flow path is set to have a sufficiently great aspect ratio to prevent such thermal impact. In detail, the width of the heating flow path is made to be three times greater than the height thereof. Namely, the heating flow path has a flat shape, which is contributive to increasing the heating area per unit volume and thus increasing heating efficiency and flow rates. Accordingly, bubble absorption and bubble growth on the heating surface can be suppressed, thereby preventing the ceramic heater 102 from experiencing thermal impact. However, when the width of the heating path is increased, the width of the ceramic heater 102 is also increased; namely, a bigger ceramic heater 102 needs to be used. Using a bigger ceramic heater 102 may be contributive to preventing thermal impact resulting from bubble generation; however, it also increases unit volume and manufacturing costs.
Besides, this document discloses using a plurality of ceramic heaters 102. However, since the plurality of ceramic heaters 102 have the same calorific value, a waste of heat may occur to thereby degrade heating efficiency.